Semiconductor devices such as integrated circuits (ICs) or large-scale integrated (LSI) circuits are generally produced by facilities provided by semiconductor manufacturers because the introduction of such facilities has lowered a barrier to entry in fabrication of the semiconductor devices. This has globalized manufacturing bases of the semiconductor devices. As a result, the price of semiconductor devices has become extremely low. In addition, a micro-electro-mechanical system (MEMS) technology utilizing a manufacturing process for semiconductor integrated circuits has enabled mass-production of sensors having consistent characteristics such as complementary metal-oxide semiconductors (CMOS) to be incorporated in semiconductor devices. The current sensor production facilities are mainly diverted from such semiconductor (IC or LSI) production facilities. In the manufacturing process for semiconductor integrated circuits, a temperature calibration process is necessary for a sensor to be calibrated in order to convert reactions detected by the sensor into a physical value such as a voltage. Such temperature calibration is generally conducted by comparing the reaction detected by the sensor with a standard of measurement.
Note that the sensor in this case is a temperature-dependent sensor such as a pressure sensor or a temperature sensor that is capable of outputting a measured value coupled with an expected temperature change. The temperature calibration of the temperature-dependent pressure sensor is generally carried out by a testing staff member or a user, who places the pressure sensor into a tester to compare pressure values output according to temperature changes in the tester with the data on the existing pressure values of the pressure sensor. The temperature sensor may be a thermocouple, a platinum resistance thermometer sensor and a thermistor. Among these, the thermocouple that is low cost and is capable of measuring a wide range of temperature is selected as a example of the temperature sensor for illustration of the temperature calibration below. A thermocouple is a temperature sensor composed of two different metallic wires (a pair of wires) either ends of which are connected. The thermocouple composed of the pair of metallic wires is configured to measure extremely feeble thermoelectric power generated in proportion to a temperature difference between either end of the pair of metallic wires and output a temperature value corresponding to the measured thermoelectric power. That is, this kind of temperature sensor outputs thermoelectric power in proportion to temperature change. Such temperature-dependent sensors may generally need temperature calibration in order to measure temperature accurately. A typical temperature calibration technique for the temperature-dependent sensors is as follows. A temperature sensor (i.e., thermocouple) is placed in a thermostatic chamber under a constant environment, and the temperature inside the thermostatic chamber is changed. The thermoelectric power output by the thermocouple is then measured while the temperature inside the thermostatic chamber is changed. The measured thermoelectric power output by the thermocouple is compared with the standard value of the thermoelectric power corresponding to the temperature change. The temperature calibration of each of temperature devices is conducted by utilizing this comparison value as a compensation value.
Japanese Patent No. 4178729 (hereinafter called “Patent Document 1”) discloses an example of the temperature calibration technology for a thermal analysis device utilizing a thermocouple as a temperature sensor. In the temperature calibration technology disclosed in Patent Document 1, a standard temperature material having a known phase transition temperature and a thermocouple are placed inside a heater. When temperatures of the standard temperature material having a known phase transition temperature and the thermocouple in the heater are gradually changed, an endothermic reaction of the standard temperature material may be observed at a temperature around a melting point of the standard temperature material. The endothermic reaction of the standard temperature material is detected as a point of inflection in a linear output change of the thermocouple. A temperature detected at the time where the point of inflection is detected is determined as a standard temperature that corresponds to a melting-point temperature, and a temperature value of the thermocouple is calibrated utilizing a correction value computed based on the determined standard temperature.
Japanese Patent Application Laid-Open Publication No. 2-039213 (hereinafter called “Patent Document 2”) discloses another example of the temperature calibration technology. In the temperature calibration technology disclosed in Patent Document 2, a heater connected in series with a high temperature pressure device. With this technology, the heater is configured to control power applied to the high temperature pressure device while detecting the temperature inside the high temperature pressure device. Thereafter, the heater continuously heats the high temperature pressure device until phase transition occurs in the standard temperature material, and the temperature at which the phase transition has occurred in the standard temperature material is detected based on the electric resistance of the heater or the voltage-current change in the heater when the phase transition has occurred in the standard temperature material. The temperature calibration of the high temperature pressure device is conducted based on the power applied to the high temperature pressure device when the phase transition has occurred in the standard temperature material.
However, in the temperature calibration technology disclosed in Patent Document 1, since the standard temperature material is placed inside the heater in a temperature calibration process, the calibration accuracy of the thermocouple may vary with a positional accuracy of the standard temperature material. That is, the positional accuracy of the standard temperature material may need improving in order to increase the calibration accuracy of the thermocouple. As a result, a capital investment may be required for improving the positional accuracy of the standard temperature material, which may result in an increase in manufacturing cost. In addition, in the temperature calibration technology disclosed in Patent Document 1, when the temperature calibration is conducted after the incorporation of the temperature sensor in a product, a user needs to remove the temperature sensor from the product. Accordingly, the temperature calibration itself may become a cumbersome task for the user. Further, in the temperature calibration technology disclosed in Patent Document 2, since the heater is electrically connected to the phase change material in series, electric conductivity in the phase transition material may be changed by the phase transition of the phase change material in addition to the electric conductivity change in the heater. Accordingly, even if the temperature calibration is conducted based on the temperature detected at which the phase transition has occurred in the phase change material, the accuracy of the temperature calibration may be lowered due to an adverse effect from the electric conductivity change in the heater.
Further, either of the disclosed technologies may require a large-scale facility having a constant temperature environment controlled based on a temperature standard. Moreover, since high-precision sensors such as temperature sensors or humidity sensors configured to absorb heat require highly accurate temperature calibration, a complicated temperature calibration process that is generally required for the high-precision sensors may need to be incorporated in the manufacturing process compared to the temperature calibration for general-purpose sensors, the manufacturing process of which includes no complicated temperature calibration process. Accordingly, the high-precision sensors need to be transferred inside a constant temperature chamber that maintains a constant temperature, and the temperature calibration is conducted by gradually changing the internal temperature in small steps, which may result in low production efficiency. Thus, this may be a bottleneck of a mass-production manufacturing process of the above-described high-precision sensors compared to transmission devices or optical devices having a simpler configuration the settings of which are much simpler than those of the high-precision sensors. Therefore, it may be difficult to reduce the manufacturing cost. The high-precision sensors further require additional cost for the temperature calibration, and hence the cost of the high-precision temperature sensors that require the temperature calibration may be several to dozens times the cost of the temperature sensors that require no temperature calibration. In particular, in order to produce much higher-precision sensors, higher cost and more time may be required for conducting highly accurate temperature calibration.
Further, despite the fact that the currently produced sensors are widely used, not many high-precision sensors are mass-produced compared to mass-produced general-purpose semiconductor devices, due to the slow progress of the temperature calibration technology. Thus, it may be most effective to eliminate the temperature calibration process itself entirely from the manufacturing process. It is preferable that the temperature calibration be easily and simply conducted every time the users use the high-precision sensors in order to maintain high accuracy of the high-precision sensors. However, it may be practically difficult for the users to carry out the temperature calibration after the shipping of the sensors. Thus, there is demand for an electric element capable of conducting temperature calibration by itself utilizing electric signals any time, anywhere in the same manner as a general-purpose semiconductor device that is simply driven by the electric signals alone.